The occurrence of carbonyl compounds such as formic and acetic acids, and formaldehyde and acetaldehyde in the museum environment is fairly well understood. Yet, these represent only a small fraction of the volatile organic compounds (VOCs) that can occur in indoor environments. This talk described a study of non-carbonyl VOCs in the museum environment.
VOCs were sampled using active and passive methods so that short-term as well as long-term variations could be studied. The sample tube was of the Perkin Elmer ATD400 type, packed with Tenax TA and Carbosieve SIII adsorbents. Analysis was by thermal desorption followed by chromatographic separation and either flame ionisation or mass spectrometric detection.
In the passive sampling mode tubes were exposed for between three days and four weeks. It was assumed that all VOCs had approximately the same uptake rate of 0.5 mL/min, and the compounds detected were quantified as ng toluene equivalents. The rationale was to try and identify as many compounds as possible in the environments tested.
Passive sampling VOC measurements were made in about 40 display and storage cases at the Victoria and Albert Museum. Metal and solid wood cases generally only contained the same range of compounds that were present in the gallery ambient atmosphere, and did not appear to contribute any VOCs themselves. Composite wood cases contained a number of compounds likely to have been derived from wood and veneer drying, such as the C3-C9 aldehydes, alpha-pinene and 3-carene. Some of the most modern cases, constructed principally of metal and glass had in fact the highest VOC concentrations, with 100s-1000s mg/m3 of toluene, xylenes, ethyl benzenes, butyl acetate and 2-ethoxyethyl acetate often present. These compounds may occur as solvents used in case manufacturing processes, and also from surface coatings such as paints and lacquers.
Active sampling measurements were made using an autosampler that allowed 24 tubes to be sampled in sequence. Two autosamplers were available, and were used, with one tube sampled every four hours, to collect a full week's worth of data in a gallery undergoing construction. The VOC concentration was found to correlated with the times that work was taking place. In a study room, where there was no special work taking place, the VOC concentration was largely constant throughout the week.
Active sampling was also used to measure the VOC concentration inside and outside a display case. It was found that when a chlorinated solvent was accidentally introduced to the gallery atmosphere, this was detected in the case atmosphere within two hours. The gallery concentration was more rapidly dispersed than that of the case, so a situation was reached where the case concentration temporarily exceeded the gallery concentration.
Although it is thought that the VOCs detected in this study are unlikely to be harmful, a surprisingly large number of compounds were detected, and in display cases these often occurred at high concentrations, up to the low 1000s mg/m3. Compounds such as esters, alcohols and hydrocarbons in this VOC cocktail are probably responsible for much of the odour associated with display cases, therefore odour cannot be considered a reliable guide to whether a case atmosphere contains harmful carbonyl compounds or not.
Passive : Exposure time is for 3 days - 4 weeks and it has an uptake rate of 0.5 mL / min. Used as a semi-quantitative method as it uses the same diffusion coefficient for all VOCs. The components are quantified as ng toluene equivalent.
Active : Two adsorbents are used. An autosampler is used which allows 25 tubes in sequence. It is fully quantitative for 27 target compounds which are analysed by GC-FID.
The VOCs in the museum environment are complex and include alkanes, aromatics, chloronates, terpenes, and oxygenates (mainly found in museum cabinets than in ambient air). A variation in the VOC concentration was found to correlate with construction activity in the gallery. The highest levels of VOCs were found in a new cabinet only 3 months old. The pollutants measured here included oxygenates, butyl acetates, butyl formates etc. The same cases, which were 3 years old, no longer had the oxygenated VOCs.
|Solid wood cabinets||ambient VOC levels only|
|Composite wood cabinets||C3 - C9 found, alpha-pinene, 3-carene, camphene (may react with O3 to produce carbonyls)|
|Modern cabinets||toluene, xylenes, ethyl benzenes, butyl acetate, 2-ethoxy ethyl acetate, methyl methacrylate, methyl acetate|
|Metal||ambient VOCs only|
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© April 25th, 2000